Modelling petroleum migration through microcrack propagation in transversely isotropic source rocks

Abstract

SUMMARY To investigate primary petroleum migration through microfracturing of source rocks, we develop a theoretical multiphysics model incorporating simultaneous generation of oil and gas from kerogen, elastic anisotropy of the source rock and propagation of microcracks filled with oil and gas. The variations of excess fluid pressure in the crack and crack propagation distance with time are determined. A detailed parametric analysis is performed to study the sensitivity of petroleum migration behaviour to changes in the input parameters including kerogen type (chemistry of kerogen to oil/gas conversion), elastic anisotropy of source rocks, geothermal gradient and burial rate. Numerical results show that a microcrack in type III kerogen-bearing source rocks can attain greater length than in rocks containing type I and II kerogen which have higher oil potentials and transform to oil/gas much faster than type III kerogen. Elastic anisotropy of source rocks has a profound influence on the crack propagation distance, but only a marginal effect on the duration of crack propagation and the excess fluid pressure. The simulation also shows that higher geothermal gradients and fast burial reduce the crack propagation duration significantly, but excess pressure and final crack length are not sensitive to the variations of geothermal gradient and burial rate.